This invention relates to a apparatus actuated by vibratory energy, such as seismic energy to switch related fluid or electric circuits and, more particularly, to an apparatus normally held in a mechanically balanced state and actuated when the mechanical balance is disturbed or upset by vibratory energy in excess of a predetermined magnitude.
Earthquake and similar vibratory phenomena are liable to cause braking of fluid pipe lines for petroleum and gases, break the grounding or interrupt electric transmission lines, thus giving rise to secondary hazards such as explosions, fires and electric lightning.
Accordingly, switching means for automatically closing or opening, a related circuit in response to vibrations above a predetermined magnitude, and which can be manually reset to the initial state for restoring a related circuit function, has been desired. Also, such a device should preferably be compact in construction and provide a long service life.
Heretofore, various types of such devices have been developed. However, those utilizing electricity or magnetism encounter difficulties in use, in view of power stoppage caused at the time of an earthquake, so that such changes and any deterioration in power service are likely to lead to operation failure at the time of an emergency and may also come difficulties relating to inspection and maintenance. Therefore their use is limited to special cases. There have also been developed various mechanical switching means for the same reasons, and these include a device which utilizes a ball placed on a horizontal surface and is adapted to roll and/or fall at the time of an earthquake, thereby closing a related circuit, and another device which utilizes a bar placed vertically on a horizontal surface and capable of being comparatively readily upset by falling down at the time of an earthquake to close a related circuit.
Although these mechanical switching means have been generally well known, they have inherent drawbacks. Firstly, they are not sufficiently sensitive to vertical vibrations, though they can respond well to horizontal vibrations. Secondly, they are liable to be actuated when they are tilted by causes other than earthquakes. Thirdly, they do not respond to vibratory acceleration. This means that they cannot ensure reliable actuation by vibrations of energy above a predetermined magnitude, and that their response time fluctuates. Fourthly, their output is not sufficiently large, and efforts to increase their output have led to increased size and weight of the whole structure due to increased weight of the ball, or bar and also due to a complicated construction.